Apparatus for recording or reproducing sound



Feb. 16,1937. G. L. YouN'r 2,071, 2

APPARATUS you RECORDING 0R 'REPnobucme sounb Eil ed Aug. 1, 1955 I60 120qa 4a o 40 so /20 Inventor. llnwinding- RPM Windihg Glen LYOUHES w W Wis Attorney Patented Feb. 16, 1937 APPARATUS roa nnconnmo on anrnonucmcsown Glen L. Younts, Schenectady, N. Y., aseignor to General ElectricCompany, a'corporation of New York Application August 1', 1935, set-m1No. 34,203

5 Claims.

My invention relates to apparatus for recording sound on a flexiblestrip or for.v reproducing it therefrom. It relates particularly toapparatus in which the two ends-oi the strip are wound on 5 tworeels,.the strip being driven alternately in opposite directions wherebyit unwinds from one reel and winds up on the other reel and vice versa,the point of recording or reproducing and the point at which the stripis driven being arranged-intermediate the two reels.

It is the object of my invention to provide an improved apparatus ofthis character by which the strip may be driven in either direction anda uniform tension be maintained'in the strip at all times andindependently of the relative amounts of the strip on the winding andunwinding reels.

My invention will be better understood from the following descriptiontaken in connection with the accompanying drawing, and its scope will bepointed out in the appended claims.

Reierring'to the drawing Fig. l is a combined circuit diagram andperspective view of one embodiment of my invention, and Fig. 2 showscurves illustrating the operation of the apparatus. I have chosen toillustrate my invention as comprising apparatus for reproducing soundfrom a previously made sound record, which record is represented asbeing formed on the opaque sound record'strip I from which the record isreproducedby reflected light, the strip being shown in the'present caseas having three parallel sound tracks on each side thereof. The two endsof -the strip are suitably secured to and wound upon the two reels 2 and3. Reel 2 is secured to the shaft 4, which is the rotor shaft of theinduction motor 5, and similarly reel 3 is secured to shaft 6, whichisthe rotor shaft or induction motor I. Both motors are arranged toproduce a torque on the reels in a direction which will 40 windthe-strip upon the reels and tension that part of the strip between the,reels. The strip is actually movedin one direction or the other by thedrum 8 over which the strip passes intermediate the reels. The drum 8 isconnected through the shaft 9 witha suitable driving motor, preferably asynchronous motor "I, which is provided with the reversing switch llwhereby the drum isandhence the sound strip may be moved in eitherdirection at the will of the operator.

Any suitable means may be employed for reproducing the sound recorded onthe strip. By way of illustration I have represented at H a portion or areproducing means comprising the lamp IS, the condensing lens 16 bywhich a spot 56 of light is thrown upon a portion of the strip engagedby the drum 8. Directed towardthe illuminated spot on the strip is theoptical system I! including a slit or other suitable means by whichlight irom'a narrow band extending across one of the sound tracks on thestrip may be di- 5 and translating the amplified output thereof intosound.

The two induction motors 5 and 1, which are similar in construction, areof the wound secondary type. In the form illustrated by way of example,these motors have their stators com- 20 prising wound single phasesecondaries and have three phase rotors that connect through the sliprings i9 and the switch 20 with the three phase source of supply 2|,which, for example, may be a 110 volt, 60 cycle source. Connected inseries 25 with each motor secondary is the resistor 23, the inductor 24,and the capacitor 25, and the value of each of these three elements issuch that the total resistance, inductance, and capacitance in the motorsecondary circuit produces a condition 30 of resonance when the rotorisat a standstill or nearly so. Under these circumstances, it will be seenthat each motor produces a maximum torque when the reels are atapproximate standstill, which torque decreases as .the speed of the 35reels increases. While I have shown and described the motors as havingthe wound second-. aries on their stators, it. will be understood thatif desired they have the wound secondaries on their rotors in accordancewith common con-- 40 struction.

Assuming the speed of the strip to'be that commonly employed, namely,feet per minute, and the strip tension to be 0.5 pound, the relation ofthe torque to angular speed of the wind- 45 mg and unwinding reels isshown by the curves 2'! and 28 respectively which show the relationbetween the torque and the speed .01 the reels for constant tension andvelocity of the strip. Em-

ploying reels having 5- inch hubs and with ap- 5 proximately 450 feet ofstrip. the system operates between polnts a and b, point 0 correspondingto the speed of thereel when full and point 12 corresponding to thespeed of the reel when empty. Obviously, it the reels have hubs of dif-.55

ferent sizes, and if a diflerent length of strip is used, points a and bwill have different locations on the curves.

These curves have substantially the same shape over the operating rangeas the curve rep-' resenting the relation between the current taken byeither motor (torque being proportional to current, neglecting frictionand secondary iron loss) and motor speed. Taking a value of 're-' sister23 such that the total resistance in the secondary circuit will limitthe motor current to a safe value when the motor is stalled and will Iexert a torque of approximately 5 inch-pounds,

the amount of the inductance of inductor 24 plus the inductance of thesecondary winding should be 0.0278 times the total resistance in thesecondary circuit and the amount of capacitance of the capacitor shouldbe 0.0633 times the same total resistance.

With reels having 5 inch bulbs the above-mentioned current-speed curveis represented by the dotted line 30. This curve, it will be seen, veryclosely approximates the curves 2'! and 28- over the operating range aswell as on either side thereof.

. It will be seen that with the apparatus which I have devised anddescribed above the strip is moved in either direction under the controlofthe drum and by the use of induction motors" having wound secondariestuned to-resonate at zero or approximately zero speed for driving thereels, the tension of the strip is maintained constant at all times, thetorque of each reel being automatically varied forthat purpose inaccordance with the rotative speed of the reel.

Withthe strip at a standstill and with ne reel empty and the other fulleach motor exerts I the same torque, which is almost two and chew halftimes the torque required by the full reel at full speed and is fourtimes the torque re-' quired by the empty reel at full speed. Thus thereis an unbalance of forces acting on the strip, the greater force tendingto start the strip toward theempty reel; however, when full speed isreachedthe forces balance. A very desirable starting characteristic thusis inherent in the system. The resulting additional strip tension due tothe above-described greater forces at starting is of advantage intending to hold the strip more snugly against the driving drum. 7 I havechosen the particular embodiment described above as illustrative of myinvention and it will be apparent that various other modificationsmay-be made without departing from the spirit and scope of my inventionwhich modifications I aim to cover by the appended claims.

What I claim as new and desire to secure by Letters Patent of theUnitedStates, is:

1. In combination, a reel upon which onev end of a flexible strip isarranged tobe wound, a

driving member arranged to engage the strip foralternately withdrawingit from the reel and.

for moving it toward the reel and a motor connected with said reel to.apply a torque thereto for causing a'substantlally uniform-tensions alltimes in said strip regardless of the direction. of movement of thestrip and the depth'of winding of the strip on the reel, said motorhaving rotor andstator elements, one of said elements tension the striptherebetween, said motors each having one element providing a rotatingfield and the otherlelement having a winding provided with means formingtherewith a circuit tuned to resonance at approximately zero motorspeed.

.3. In combination, a plurality of reels upon which opposite ends of'asound record strip are arranged to be wound, -a. driving member arrangedto engage the strip between said reels for moving the strip in eitherdirection, means for maintaining the tension in the strip equal onopposite sides of the driving member comprising a polyphase mntorconnected with each of said reels tending to tension the strip betweenthe reels and the." driving member. eachof said motors having a woundsecondary and a control circuit connected with each secondary tuned toresonate at substantially zero rotor speed.

4. In apparatus of the character described, a plurality of reelsuponwhich opposite ends of a sound record strip are arranged to be ,.wound,I

a driving drum arranged to engage t'he strip ata point intermediate saidreels, means for rotating the drum in either direction at will, meansfor maintaining the tension in the strip 1 equal on opposite sides ofthe driving member comprising a induction motor connected with, eabhreel and tending to drive the reel in a direction to tension the stripbetween the reels, eachrof said motors having a wound secondary andjanexternal circuit including resistance, inductance and capacitance, saidcircut and secondary forming a tuned circuit resonant at zero motorspeed.

5. In combination, a plurality of reels upon which opposite ends of asound record strip are arranged to be" wound, a driving member arrangedto engage the strip between said reels for moving it alternately inopposite directions and a driving motpr connected with each: reel forproducing a substantially equal tension in the strip at opposite sidesof said member and uniform tension in the strip independently of thedirection of movement thereof and the depth of winding on the respectivereels. said motors each comprising an element providing a rotating iieldand a cooperating element having a winding provided with means formingtherewith a circuit to resonance at approximately sero motor speed.

. I GLEN L. rooms.

